With the advent of networked stand-alone computer work stations, a need has arisen for efficient, reliable, and cost effective power sources from which workstations and their associated peripheral equipment may receive electrical power. Since each work station may be required to process hundreds of transactions a minute, many businesses typically attempt to avoid equipment downtime. Hence, numerous methods of providing power to workstations have been developed.
One approach for providing highly reliable power to workstations is via direct wiring from a central power distribution box protected by circuit breakers. In this approach, a common three wire bundle is often strung from a circuit breaker to a receptacle. The receptacle typically provides the needed electrical connectivity for one or two pieces of equipment, and the circuit breaker usually prevents the circuit from being overloaded. Clearly, this approach often provides the highest reliability, as each work station is powered by a dedicated wire. However, as additional equipment is added to a work station, the power needs at a particular location may change such that additional receptacles are needed, thereby typically requiring the stringing of additional power lines and other required components. Thus, the direct wiring method often proves to be cumbersome, expensive, and inefficient.
Another approach at providing power to workstations is via power strips. Power strips commonly provide multiple receptacles which are connected in series to a commonly provided 110 volt electrical receptacle. Often these power strips are limited to 15 amps and may provide only 6 receptacles. While currently available power strips address the need to connect multiple pieces of equipment to a common electrical source, many drawbacks still typically exist.
One problem with currently available power strips is the inaccessibility of the internal wiring which commonly increases the difficulty in preforming load determinations. Load determinations are important because often it may be necessary to power additional electrical components via a power strip which is already providing electrical power to other vital components. Since the addition of a single component may overload a power strip, flip a circuit breaker, power off critical equipment, and ultimately result in hundreds or even thousands of lost transactions, system integrators are extremely cautious when connecting additional electrical components to a power strip already in use. As such, system integrators are often required to measure the load upon a circuit before connecting additional components. Since the load upon a power strip may not be directly measured by placing a suitable sensor around the wire bundle which connects the power strip with a host electrical receptacle, a direct measurement must often be made by accessing a power distribution panel, removing the panels covers, and determining the electrical current load at a specific circuit breaker. However, this approach, while effective, is extremely time consuming, and raises unique safety concerns. Since the electrical power present at a central power distribution system may be lethal if the wrong nodes are touched by a hand, screw driver, or the like, this approach (to ensure safety) often requires a certified electrician to access the circuit breaker and determine power loads whenever an additional electrical component needs power.
Since it is often highly undesirable to access the internal wiring of a circuit breaker to determine the load upon a particular power strip, a power strip with a removable cover would be extremely beneficial. Numerous patents have generally disclosed removable covers on power strips, such as the approach disclosed in U.S. Pat. No. 4,930,047, issued May 29, 1990 to Gerald E. Peterson, and titled "APPARATUS FOR INTERCONNECTING COMPONENTS OF A POWER OUTLET STRIP". While the Peterson patent generally discloses a removable bottom cover which, upon removal, reveals the component parts necessary to provide electrical power to a plurality of receptacles, this approach does not allow for the internal wiring to be accessed and the current load determined while continuing to provide electricity to the connected components. In fact, the Peterson patent requires the top cover to be pried from the bottom cover in order to access the internal components. As such, a system integrator would most likely find it extremely difficult to pry the top cover away from the bottom cover while continuing to provide electrical power to connected components.
Similarly, U.S. Pat. No. 4,705,342, issued Nov. 10, 1987 to Frederick W. Schwartz, titled "ELECTRICAL EXTENSION OUTLET", generally discloses a power strip wherein a top cover is snapped into a middle piece which is fastened to a bottom cover. Moreover, the electrical components are primarily secured to the top cover and the middle piece while the bottom cover connects the power strip to a mounting surface. As such, in order to access the internal wiring, the Schwartz patent requires either the power strip to be removed from the mounting surface and the fasteners connecting the bottom cover to the middle piece removed thereby exposing the internal wiring, or the top cover pried from the middle piece and the internal wiring thereby exposed. Either of these approaches would probably be extremely cumbersome and time consuming and next to impossible when electrical components are plugged into and receiving power from the power strip. As such, a power strip which allows for easy access to internal wiring such that electrical current loads may be determined without interrupting the provision of electricity is needed.
Another problem with currently available power strips is the uneven loading of electrical current upon the receptacles. A power strip is typically designed such that the first receptacle is connected to the incoming power source and each subsequent receptacle is connected thereafter in series. As such, the first receptacle will experience the current load of the subsequent receptacles. For example, if a power strip contains 10 receptacles connected in series, each drawing a maximum 1.5 amps, the receptacle closest to the incoming power source will experience 15 amps upon it.
This high current source may result in excessive current entering equipment attached to this first receptacle, or may result in the receptacle "burning out". As a result, numerous approaches have attempted to address this uneven current loading by providing a common bus connected in parallel to a plurality of receptacles. One such approach is disclosed in U.S. Pat. No. 4,113,334, issued on Sep. 12, 1978 to John C. Instone, titled "ELECTRICAL OUTLET STRIP". The Instone patent discloses a wire connected in parallel to a series of leads such that the incoming power will come into contact simultaneously with the leads connected to each receptacle. As such, this approach primarily depends upon one common bus wire to carry all the current for the receptacles. Should this common bus wire fail for whatever reason, all the power to the receptacles downstream of the failure may be interrupted. Since reliable, evenly distributed, electrical power is critical in computer operations centers. a power strip which does not rely upon a single bus bar or wire is needed.
Another concern with power strips designed for the computer workstation environment is that the power strip does not allow the electrician to replace a malfunctioning receptacle without having to shut off power to the remaining receptacles. As mentioned, eliminating power for just a few minutes or seconds could be devastating to the operations of a business. U.S. Pat. No. 4,318,156, issued Mar. 2, 1982 to Michael J. Gallagher, titled "Portable Distribution Box" generally discloses a related system. The Gallagher patent discloses a plurality of receptacles which are connected via a circuit breaker, contained within the "Power Distribution Box", to a power cord receiving power from an external source. Each receptacle may be individually turned on or off by flipping an associated switch. While this approach provides for the removal of a receptacle by flipping the associated switch to the off position, it commonly does so at great expense. The Gallagher approach specifies a circuit breaker, a switch, and a pilot (or similar indicator light) which, if utilized in a large computer workstation environment, may be cost prohibitive, and time consuming and expensive to repair. Thus, an inexpensive and electrically simple power strip is needed which allows for a receptacle to be replaced without interrupting the provisioning of electrical power to the remaining receptacles.
Another attempt at providing a power strip which allows for the replacement of a single receptacle without disrupting the power to the remaining receptacles is disclosed in U.S. Pat. No. 5,350,310, issued Sep. 27, 1994 to Ken-Ching Chen, titled "Socket Terminal", and in U.S. Pat. No. 5,429,518, also issued on Jul. 4, 1995 to Ken C. Chen, titled "Socket Terminal". Both of these patents disclose a power strip wherein each receptacle is positioned above a common bus bar from which metal tabs extend. As each receptacle is rotated clockwise, the connector portions of the receptacle comes into contact with the tabs extending from the corresponding bus bars, thereby completing an electrical connection. Similarly, by rotating each receptacle counter-clockwise, a receptacle's connectors will be removed from contact with the tabs, thereby disrupting the electrical connection with that receptacle. In actuality, however, the Chen approaches depend upon a common bus, and the extension of tabs therefrom, such that whenever a tab may fail for whatever reason, the entire bus would probably have to be powered down to allow reattachment of a tab, by soldering or the like, to the bus. Additionally, the replacement of a single receptacle may result in the displacement of the remaining receptacles because each receptacle is retained by a flange in contact with the top cover of the power strip. As the top cover is removed, each receptacle is no longer securely positioned. In order for receptacles to be removed from a Chen patented device, the power strip would probably have to lay flat on its bottom surface (i.e. it could not be vertically positioned, or be positioned on its side), and the top cover carefully removed such that none of the remaining receptacles were dislodged. Thus, the Chen patents do not disclose a power strip which allows the replacement of a receptacle without interrupting the power provided to the remaining receptacles.
Another problem frequently encountered when power strips are utilized in computer workstation environments, is the overloading of the circuit due to additional equipment being plugged into the power strip. Often radios, clocks, fans, and similar electrical components are plugged into the nearest available electrical outlet which may be a power strip whose receptacles are not all being used. The mere fact that all the receptacles in a power strip are not being used does not mean the power strip can carry additional electrical loads. Workers are often ignorant of this fact, and occasionally plug components into the fully loaded power strip which overloads the circuit, trips the breaker, and catastrophically powers down critical equipment receiving electricity from the power strip. Thus, a power strip which strictly limits access is needed.
Therefore, it can be appreciated that there exists a need for a power strip which allows for the easy determination, at the power strip itself, of the current being drawn by the attached equipment, while providing a highly reliable, evenly distributed current load across a plurality of receptacles, and allows the replacement of a receptacle without interrupting the power being provided to the remaining receptacles.